Typically, commercially available compositions for forming chromate coatings, which are also known as a chromate treatment agents, comprises water as a solvent and contain incorporated therein a hexavalent chromium compounds as a main ingredient in combination with suitable proportions of a fluoride, a mineral acid, a carboxylic acid, a surfactant and other chemicals. When a work-piece, for example a zinc plated metal piece, is immersed in such a chromate treatment agent, complex compounds of tri-and hexa-valent chromiums are deposited on the surface of the work-piece to form a chromate coating. Such chromate treatment agents are disclosed in U.S. Pat. Nos. 3,053,693; 3,501,352; 3,808,057; 3,857,739; 3,895,969; and 3,907,610.
U.S. Pat. No. 3,053,693 which issued on Sept. 11, 1962 to Ludwig K. Schuster and Alfonso L. Baldi discloses a coating mixture in the form of an aqueous dispersion of a non-waxy hydrophobic resin containing a dissolved chromium compound from the class consisting of chromic acid which contains hexavalent chromium and the water-soluble dichromates of metals which have a valence greater than one.
U.S. Pat. No. 3,501,352 which issued on Mar. 17, 1970 to Vinod D. Shah discloses a composition containing a chromium chromate complex. The chromium chromate complex is prepared from aqueous chromic acid solutions which containn hexavalent chromium.
U.S. Pat. No. 3,808,057 issued on Apr. 30, 1974 to Wolfgang Lobenski, Heiny Paul Schapitz and Hans-Peter Wessel. This patent discloses a method for coating metal articles by first depositing a layer of zinc on the metal article then submerging the article in a chromic acid solution.
U.S. Pat. No. 3,857,739 issued on Dec. 31, 1974 to Michael Ward Prust and Wayne Charles Glassman and discloses a process for producing a chromium protective coating on zinc. The process utilizes chromium in the water soluble hexavalent form.
U.S. Pat. No. 3,895,969 which issued on July 22, 1975 to Russell C. Miller discloses a chromate depositing solution which contains hexavalent chromium.
U.S. Pat. No. 3,907,610 issued on Sept.
23, 1975 TO Hidehisa Yamagishi, Hirokuni Mizuno, Yoshitaka Kashiyama and Yasuhiro Toyoda. This patent discloses a process for treating metal which uses hexavalent chromium.
Many heavy metals and elements, such as lead, mercury and arsenic for example, are dangerous when ingested or absorbed by animal tissues. These materials are environmentally undesirable and great care is taken to insure that they do not pollute the air or water. Hexavalent chromium compounds are environmentally undesirable because of monochromium trioxide is deliquescent meaning that it absorbs moisture. Monochromium trioxide absorbs water and forms undesirable chromic acid. Conversely, bivalent and trivalent chromium compounds are environmentally acceptable.
It is therefore desirable to provide a chromate treatment agent which contains and produces no hexavalent chromium compound and which does not pose an environmental concern.